Analysis And Identification Of Rotor Winding Inter-turn Short Circuit Fault In Turbine Generator Based On Field-circuit Coupling

Rotor inter-turn short circuit fault is very common among turbo generator which is in operation. When the fault occurs, the effective turns of the exciting winding in fault pole decreases, magneto motive decreases, and the magnetic field near the two poles become asymmetrical. On the one hand, asymmetrical magnetic field can make the electromagnetic force distribute unevenly on the rotor, then unbalanced electromagnetic force and rotor vibration appear. On the other hand, asymmetrical magnetic field can induce different inductive potentials in the two parallel branches of stator, then unbalanced voltage appears. So, it will provide assistance for failure diagnosis to analyze the fault from the three aspects: asymmetrical magnetic field,unbalanced electromagnetic force and unbalanced voltage.In this paper, a 2D transient finite element field-circuit coupling model of a generator is established, and its validity is verified. Analyze the magnetic field asymmetry in this angle: flux density variation of one point in air gap, obtain the air gap flux density curves of normal and fault conditions, and compare the curves from the three aspects:short circuit position, short circuit number of turns and shot circuit slot position. Conduct spectral analysis to the above curves, and find the change rule of fundamental wave and each harmonic. Let the air gap flux density derivative of normal condition subtract it of fault conditions respectively, and get the flux density derivative difference curves of various situations, which reflect the difference of slot leakage flux. Compare them from the above three angles, and find their influence on slot leakage flux.Apply the Maxwell stress tensor method for the simulation calculation of rotor's unbalanced electromagnetic force, get the change rule of component forces changing with time, and discuss the change rule of unbalanced electromagnetic force curves' amplitude, waveform and harmonics from the above three angles, and it can provide basis for rotor vibration research. Analyze the unbalanced voltage under rotor inter-turn short circuit fault and air gap eccentric fault, and find the influence on unbalanced voltage of short circuit position, short circuit number of turns, position of short circuit slot, eccentric distance and eccentric angle. Analyze the unbalanced voltage under different rotor inter-turn short circuit faults accompanying air gap eccentric fault, and find the influence of short circuit number of turns and position of short circuit slot on unbalanced voltage under combined failure.